CocosDenshion SimpleAudioEngine pan setting too course

cocos2d-x C++
1

I’m testing my game on the Mac (I can’t test on a device at the moment).
I play a sound with

CocosDenshion::SimpleAudioEngine::getInstance()->playEffect("monoSound.caf", false, 1, pan, 1);

When pan is any positive number I hear the sound on the right channel.
When pan is zero I hear the sound on both channels
When pan is any negative number I hear the sound on the left channel.

There’s no ‘in-between’. It’s either all left, all right or central - but I want to have fine-grained control over the position.

Is this possible?

P.S. If I run on the emulator it works fine